Metathesis is a catalytic reaction generally known in the art that involves the interchange of alkylidene units among compounds containing one or more double bonds (e.g., olefinic compounds) via the formation and cleavage of the carbon-carbon double bonds. Metathesis may occur between two like molecules (often referred to as self-metathesis) and/or it may occur between two different molecules (often referred to as cross-metathesis). Self-metathesis may be represented schematically as shown in Equation I.R1—CH═CH—R2+R1—CH═CH—R2R1—CH═CH—R1+R2—CH═CH—R2  (I)
wherein R1 and R2 are organic groups.
Cross-metathesis may be represented schematically as shown in Equation II.R1—CH═CH—R2+R3—CH═CH—R4R1—CH═CH—R3+R1—CH═CH—R4+R2—CH═CH—R3+R2—CH═CH—R4+R1—CH═CH—R1+R2—CH═CH—R2+R3—CH═CH—R3+R4—CH═CH—R4  (II)
wherein R1, R2, R3, and R4 are organic groups.
In recent years, there has been an increased demand for environmentally friendly techniques for manufacturing materials typically derived from petroleum sources. For example, researchers have been studying the feasibility of manufacturing waxes, plastics, and the like, using natural feedstocks, such as vegetable and seed-based oils. In one example, metathesis catalysts are used to manufacture candle wax, as described in PCT/US 2006/000822, which is herein incorporated by reference. Metathesis reactions involving natural feedstocks offer promising solutions for today and for the future.
Natural feedstocks of interest typically include, for example, natural oils (e.g., vegetable oils, fish oil, animal fats) and derivatives of natural oils, such as fatty acids and fatty acid alkyl (e.g., methyl) esters. These feedstocks may be converted into industrially useful chemicals (e.g., waxes, plastics, cosmetics, biofuels, etc.) by any number of different metathesis reactions. Significant reaction classes include, for example, self-metathesis, cross-metathesis with olefins, and ring-opening metathesis reactions. Representative examples of useful metathesis catalysts are provided below. Metathesis catalysts can be expensive and, therefore, it is desirable to improve the efficiency of the metathesis catalyst.
Catalyst efficiency and product conversion can vary dramatically depending on the purity of the feedstock that is being metathesized. One of the challenges with using natural feedstocks is that naturally-derived feedstocks may include impurities, sometimes in trace amounts, that do not exist in petroleum feedstocks. These impurities often react with the metathesis catalyst and may drastically affect the efficiency of the catalyst and metathesis reaction. Moreover, the presence and level of various impurities in natural oils may vary from batch-to-batch, depending, for example, on the geographic location of the harvest, and even on the specific field of harvest as well as other growing conditions.